This invention relates to a thermoplastic resin composition having an excellent balance in various properties, and a molded product thereof. More specifically, this invention relates to a thermoplastic resin composition in which mechanical strength, heat resistance, moldability, appearance of a molded product, chemical resistance and dimensional characteristics are excellent by making a portion in which a non-crystalline thermoplastic resin (e.g. a non-crystalline thermoplastic resin comprising a polyphenylene ether (hereinafter referred to as "PPE") or PPE and an aromatic vinyl compound polymer) takes a structure forming a matrix and a portion in which a crystalline thermoplastic resin (e.g. a crystalline thermoplastic resin comprising a polyolefin type resin) takes a structure forming a matrix coexist and, if necessary, making an inorganic filler exist in a specific phase, and a molded product thereof.
A polymer blend comprising a combination of two or more resins has a characteristic that a well-balanced composition can be obtained by using good properties of the respective resins and compensating undesirable properties thereof. Excellent effects in practical use can be obtained particularly by a combination of a crystalline thermoplastic resin and a non-crystalline thermoplastic resin so that various combinations thereof have been made.
A non-crystalline thermoplastic resin is an useful resin generally having excellent heat resistance and dimensional stability. For example, PPE has excellent heat resistance and impact resistance. However, PPE has extremely poor moldability so that PPE has a drawback that it is extremely difficult to carry out injection molding of PPE when it is used alone. In order to remove such a drawback, materials having a relatively good balance of moldability, impact resistance and heat resistance have been developed by formulating a polystyrene type resin into PPE, and the materials are commercially available as engineering plastics.
For example, there has been disclosed a composition of PPE and a high impact polystyrene in U.S. Pat. No. 3,383,435. In this composition, although moldability is improved, solvent resistance is poor and a balance between heat resistance and impact resistance is insufficient. Also, a composition in which impact resistance is improved by formulating a polystyrene resin and rubber or a rubber-modified polystyrene resin into PPE and making the average particle size of the rubber 0.5 to 2 .mu.m has been disclosed in Japanese Provisional Patent Publication No. 28659/1976, and a composition in which a polystyrene resin and rubber or a rubber-modified polystyrene resin is formulated into PPE and a gel fraction rate is specified has been disclosed in Japanese Provisional Patent Publication No. 460/1981. In these compositions, although impact resistance is improved, rates of sink mark and warpage after molding are large, and surface impact resistance which is practical strength is insufficient.
In the field where high rigidity is required, a non-crystalline thermoplastic resin has been filled with a fibrous inorganic filler such as glass fiber and carbon fiber or a plate-shaped inorganic filler such as talc and mica. Also in this case, a drawback that solvent resistance is poor remains unsolved and a further drawback that moldability is bad is more remarkable.
A crystalline thermoplastic resin has excellent solvent resistance and moldability and has been used in many fields. For example, a polyolefin type resin has excellent organic solvent resistance and moldability so that, for example, a polypropylene type resin has widely been used for parts for automobiles, household electric appliances and daily necessaries. However, said resin has insufficient dimensional stability due to large thermal expansion coefficient and poor heat resistant rigidity so that it cannot be used for large-sized parts in which heat resistance is required, particularly a fender and a wheel cover of an automobile, whereby its application is limited. In order to remove such a drawback, for example, a technique of formulating talc which is an inorganic filler has been studied, but when talc is formulated, there is a problem that impact resistance is lowered. For the purpose of improving a balance of dimensional stability and impact resistance described above, a composition in which talc and ethylene-propylene rubber are formulated has been disclosed in Japanese Provisional Patent Publication No. 3420/1985, and compositions in which appearance is improved by adding polyethylene have been disclosed in Japanese Provisional Patent Publications No. 49252/1984, No. 276840/1986 and No. 65223/1988, respectively. However, even in molded products using these compositions, a balance of mechanical strength, appearance of a molded product and dimensional stability is not necessarily sufficient and there is a problem that surface hardness is low.
In the field where high rigidity is required, a crystalline thermoplastic resin has been filled with a fibrous inorganic filler such as glass fiber and carbon fiber or a plate-shaped inorganic filler such as talc and mica. When said resin is filled with such an inorganic filler, there is a serious drawback that a molded product is warped.
For the purpose of obtaining a material having both of excellent heat resistance and mechanical properties of PPE and excellent solvent resistance and good moldability of a polyolefin type resin, there have been proposed compositions in which both resins are formulated. For example, it has been attempted to improve solvent resistance and impact resistance by formulating PPE and a polyolefin type resin in Japanese Provisional Patent Publication No. 7069/1967. However, in the resulting composition, the amount of the polyolefin type resin formulated is small so that a matrix substantially comprises PPE, whereby effects of improving solvent resistance and moldability are insufficient. Further, when the amount of the polyolefin type resin to be formulated is increased, compatibility of both resins is insufficient so that there is a problem that laminar peeling of a molded product is caused to lower mechanical properties. As an attempt to improve said compatibility, compositions to which a styrene-butadiene block copolymer or a hydrogenated product thereof is added have been disclosed in, for example, Japanese Provisional Patent Publications No. 225642/1988, No. 245353/1988, No. 40556/1989 and No. 93647/1989.
However, in these compositions, a matrix substantially comprises PPE or a combination of PPE and a styrene type block copolymer so that there is a drawback that characteristics of a polyolefin type resin cannot be exhibited sufficiently.
Also, a composition comprising a polyolefin type resin as a matrix and PPE having excellent heat resistance and dimensional stability being dispersed therein has been disclosed. For example, a composition having excellent molding processability, impact resistance and appearance of a molded product, in which PPE and a rubber each having a specific size are dispersed in a matrix of a propylene polymer has been proposed in Japanese Provisional Patent Publication No. 185553/1990. However, in the composition, the matrix is a propylene polymer so that excellent rigidity and heat resistance of PPE cannot be exhibited sufficiently and surface hardness is low. Thus, the composition cannot satisfy recent high level of market requirements.
In the field where high rigidity is required, the blend described above has been filled with a fibrous inorganic filler such as glass fiber and carbon fiber or a plate-shaped inorganic filler such as talc and mica. In this case, it is difficult to solve a problem of warpage of a molded product which is a drawback of a crystalline thermoplastic resin and a problem of poor solvent resistance and moldability which are drawbacks of a non-crystalline thermoplastic resin, whereby there are problems in practical use.